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          Feline Infectious Peritonitis - updated information for breeders 
          Susan Little DVM, Diplomate ABVP (Feline) 
          CFA Health Committee 

          Probably one of the most controversial areas in any discussion of FIP is Primucell FIP, the vaccine made
          by Pfizer Animal Health, available since 1991. The vaccine is a modified-live temperature-sensitive viral
          mutant licensed for intranasal use in cats at least 16 weeks of age. The manufacturer recommends annual
          revaccination although no duration of immunity studies are available. The vaccine stimulates local immunity
          and will also produce an antibody titre. Evaluation of the risks and benefits associated with this vaccine is a
          difficult venture and has engendered much controversy. 

          Since FIP is a severe and fatal disease, the safety of any vaccine is a paramount consideration. Dr. Fred
          Scott of the Cornell Feline Health Center, concluded in a recently published paper, that the risks associated
          with the Primucell FIP vaccine are minimal in most situations. He notes that the vaccine has been in use for
          7 years with no increase in the incidence of FIP. Troubling reports of a phenomenon called
          "antibody-dependent enhancement" (ADE) of infection arose from several labs, where cats vaccinated with
          FIP vaccines and challenged experimentally with virus developed accelerated disease instead of being
          protected. It is not known whether the phenomenon of ADE occurs in the real world and there is no easy
          way to find out. If it does occur, it is likely an uncommon event, but the possibility remains troubling. 

          On the other side of the issue, the benefits of the Primucell FIP vaccine appear to be small. The best
          reported efficacy for the vaccine is seen when FCoV negative cats at least 16 weeks old were vaccinated
          twice (3 weeks apart), in a study by Dr. Nancy Reeves published in 1995. In this study, FCoV
          antibody-negative cats were vaccinated before entering a large cat shelter where FIP was endemic. The
          vaccinated cats experienced a significantly lower mortality rate than unvaccinated cats. The efficacy of the
          vaccination was calculated to be 75% (preventable fraction). 

          In catteries where FIP is endemic, studies have shown the vaccine had no effect on the incidence of
          disease. One reason may be that most kittens in catteries are infected between 6 and 10 weeks of age, long
          before the 16 weeks of age the vaccine is licensed for. Once a cat is infected with FCoV, the vaccine has
          no benefit. Some cattery owners have been using the vaccine at ages younger than 16 weeks to get around
          this problem. Dr. Johnny Hoskins has outlined a vaccination protocol for catteries experiencing FIP losses
          in kittens under 16 weeks of age. He recommends giving the vaccine at 9, 13 and 17 weeks with annual
          revaccination afterward. Use of this protocol must be made with the knowledge that no controlled studies
          have been done on kittens under 16 weeks of age and that this is an off label use. It would appear that the
          use of the vaccine according to the manufacturer's directions is limited to the vaccination of FCoV
          antibody-negative cats entering high risk situations, such as catteries and shelters.

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